Use our free tool below to Convert Length instantly – meters, centimeters, inches, feet, miles, kilometers
Millimeter (mm)
The millimeter (mm) is a metric unit of length in the SI system, defined as 0.001 metre. en.wikipedia.org. The metric system was established during the French Revolution to use decimal-based measures; the metre itself was originally one ten-millionth of the Earth’s quadrant en.wikipedia.org. Millimeters are used for very small measurements (e.g. engineering tolerances, thicknesses). For scale, 1000 mm = 1 m and 1 mm = 0.1 cm. In practice, a sheet of copy paper is about 0.1 mm thick en.wikipedia.org and a human hair is roughly 0.02–0.04 mm thick en.wikipedia.org. The millimeter differs from the centimetre by a factor of 10 (1 cm = 10 mm) and from the metre by a factor of 1000.
- Differences: 1 mm = 0.001 m; 1000 mm = 1 m; 10 mm = 1 cm.
- Everyday examples: A sheet of paper (~0.1 mm) or a fingernail (~1 mm) gives a sense of millimeter scale en.wikipedia.org. Machine parts and map precision often use millimeters.
- Exercises: Convert 2500 mm to metres (2.5 m); how many millimetres are in 4.3 cm?
Centimeter (cm)
The centimetre (cm) is 1/100 of a metre en.wikipedia.org. It uses the prefix “centi-” (1/100). Like all metric lengths, it was defined by the same historical metre standard (now by light speed) en.wikipedia.org. Centimeters are practical for everyday measurements. For example, human height is commonly expressed in centimetres en.wikipedia.org, and a fingernail is roughly 1 cm wide en.wikipedia.org. In relationships: 1 cm = 10 mm and 100 cm = 1 m. The centimetre differs from the millimetre by a factor of 10 (1 cm = 10 mm) and from the metre by 100.
- Differences: 1 cm = 10 mm; 100 cm = 1 m; it is 0.01 m by definition en.wikipedia.org.
- Everyday examples: An adult’s fingertip width is about 1–2 cm; a credit card is ~8.5 cm wide.
- Exercises: Convert 150 cm to metres (1.50 m); if a room is 350 cm long, how many metres is that?
Inch (in)
An inch is an Imperial/US customary unit of length. By international agreement it is defined as exactly 25.4 millimetres (2.54 cm) inchcalculator.cominchcalculator.com. The inch traces back to the Latin uncia (“one-twelfth” of a Roman foot) and was historically defined by barleycorns (1 in = 3 barleycorns) inchcalculator.com. Its modern definition (1959) fixes 1 in = 2.54 cm inchcalculator.com. Inches are used mainly in the United States and partially in the UK for everyday measures (e.g. screen sizes, shorter building dimensions). It differs from the centimetre (1 in = 2.54 cm) and from the foot (12 in = 1 ft).
- Differences: 1 in = 2.54 cm inchcalculator.com; 12 in = 1 ft.
- Everyday examples: The width of an average adult thumb is about 1 inch. Many rulers and monitors are marked in inches, and paper sizes (e.g. 8½″×11″) use inches.
- Exercises: How many centimetres are in 36 inches? (Answer: 91.44 cm, since 36×2.54 cm)；Convert 5 inches to millimetres (≈127 mm).
Foot (ft)
A foot (ft) is an Imperial/US unit of length, defined as 12 inches. By international agreement, 1 foot = exactly 0.3048 metres en.wikipedia.org. Historically the foot varied (about 250–335 mm) depending on region en.wikipedia.org. It is still used in the US for height, construction and aviation (altitudes in feet). For comparison: 1 ft = 12 in ≈ 0.3048 m en.wikipedia.org, and 3 ft = 1 yard. A typical adult’s height is about 5 to 6 feet, and standard room height is ~8–10 ft.
- Differences: 1 ft = 12 in; 3 ft = 1 yd; 1 ft = 0.3048 m en.wikipedia.org.
- Everyday examples: A person 6 ft tall is about 183 cm. Standard door width is ~3 ft. In construction, studs and lumber are often measured in feet.
- Exercises: Convert 10 ft to metres (≈3.048 m) en.wikipedia.org; how many inches are in 5 feet? (Answer: 60 inches.)
Yard (yd)
A yard is an Imperial/US unit of length, equal to 3 feet or 36 inches britannica.com. By definition 1 yd = 0.9144 metres (derived from the 1959 agreement). It originated as a “cloth-yard” measure (37 inches) and later standardized britannica.com. Yards are used in the US/UK for short distances, e.g. in sports (“100-yard dash”) or property measurements. One yard is about as long as an adult’s stride.
- Differences: 1 yd = 3 ft = 36 in britannica.com; 1 yd = 0.9144 m.
- Everyday examples: A yardstick is one yard long. Football fields are measured in yards (e.g. “50 yard line” is 45.72 m).
- Exercises: Convert 10 yards to metres (≈9.144 m).
Mile (mi)
A mile is a large Imperial/US unit of distance. The “statute mile” is defined as exactly 5280 feet (or 1760 yards), which equals 1609.344 metres en.wikipedia.org. Its name comes from Latin mille passus (“thousand paces”), the Roman mile. The modern international mile (since 1959) is exactly 1.609344 km en.wikipedia.org. Miles are used in the US and UK for road distances and running events (e.g. a marathon is ~26.2 miles).
- Differences: 1 mi = 5280 ft; 1 mi ≈ 1.609 km en.wikipedia.org.
- Everyday examples: Major road distances in the US are posted in miles (e.g. “10 miles to city center”); a mile run is a common athletic event.
- Exercises: How many kilometres are in 5 miles? (≈8.047 km) en.wikipedia.org; convert 3 miles into feet (3×5280 = 15840 ft).